As is well-known, such devices are comprised of a plurality of pairs of coaxial rotatable rings made of permanent magnet material and located on a non-magnet mounting sleeve which is designed to be fastened to the neck of a tube. The static magnetic fields generated by permanent magnet poles located in the magnet rings are angularly adjusted such that the outer beams of three in-line electron beams are slightly shifted until they converge with the center beam at a central point behind the screen, the adjustment performed with no dynamic magnetic field generated by the deflection yoke, and thereby causing the beams to strike the correct phosphors on the screen. The magnetic rings are usually provided with ears or other means for the purpose of aiding in the manual angular adjustments. These adjustments comprise two successive operations for each magnet ring pair: first, the optimum angle between the symmetry axes of the rings of a given pair is found, and second the optimum angular location of the given ring pair is determined. The adjusting operations are repeated for each of the plurality of magnetic ring pairs. The complete adjustment operation is time-consuming and is sensitive. Frequencly the adjustment operation must be repeated by the retailer of the television receiver because the rings have been maladjusted during transporation from the factory.
Accordingly, it is desirable to simplify the adjustment operation. Therefore, enhanced mechanisms have been designed to reduce the time spent to obtain the necessary accurate adjustment of magnetic ring pairs to attain static beam convergence.
Prior-art static convergers, including those described in issued French patent applications numbered 2,224,869; 2,244,256; and 2,304,173, disclose improved adjusting assemblies in which the magnetic rings of each pair are concentrically located in the same plane. Such convergers have a toothed wheel located in the space between rings such that the wheel is rotatable around an axis which is fixed with respect to a non-magnetic mounting sleeve. Therefore, when one ring of the pair is rotated in one direction, the other ring of the pair is automatically rotated in the other direction. Using this mechanism, the optimum angle between the symmetry axes of the two rings is easily attained. But such an assembly requires concentric magnet rings of unequal diameter and, therefore, the magnet poles cannot be equidistant to the tube axis. In addition, an intermediate toothed wheel meshing with associated teeth on the rings both increases the production costs and decreases the reliability since a significant friction force must be generated between the magnet rings of each pair to avoid disadjustment during transportation of the television set.
In previously issued French patent application 2,290,029, assigned to the same assignee as the present invention, another type of mechanism for static convergence is disclosed. In accordance with one of the described embodiments, the rings are fabricated using a non-magnet material and magnets are fastened on the ring periphery. A single means is provided on each ring pair for adjusting both operations during the tuning of each ring pair. A member fastened on the periphery of one of the pair of rings houses a rotatable rod which is radially positioned. A knob is attached to the first end of this rod and a pinion is attached to the second end such that the pinion meshes with gears provided in the periphery of the second ring. Therefore, by rotating the knob around its axis, the optimum angle between the rings of one pair may be easily attained, and by angular rotation of the knob around the tube axis both rings are simultaneously rotated without changing the previously obtained angle between the rings.
The described mechanism has been improved in order to ease the tuning adjustments by means disclosed in U.S. Pat. No. 4,050,042 and in German patent application 27 24 061. In such mechanisms, the amplitude of the friction forces is determined by the pressure between adjacent rings after adjusting of all the rings of the complete device. Also, minimum length of the complete device is limited to a relatively large value because each pair of magnetic rings requires two non-magnetic rings.